pitted scar (IOM, 1999). Any type of reaction that is not a major reaction is considered equivocal and indicates that revaccination is necessary.

In 1999, the Working Group on Civilian Biodefense, an expert panel convened by the Center for Civilian Biodefense Studies at Johns Hopkins University (now the Center for Biosecurity at the University of Pittsburgh Medical Center) acknowledged that a deliberate release of smallpox virus was in the realm of possibility and that such an event would require widespread vaccination (Henderson et al., 1999). However, until the fall of 2001, smallpox vaccine had FDA approval only for use in a very small group of laboratory workers, and a limited supply of smallpox vaccine existed under the control of the Centers for Disease Control and Prevention (CDC), containing the New York City Board of Health (NYCBH) vaccinia virus strain grown on scarified calves, and produced by Wyeth laboratories under the trade name Dryvax (Henderson et al., 1999).

The policy changes that revived civilian smallpox vaccination and vaccine research, development, and production in the United States are discussed in Chapter 2.

The Vaccine Supplies Available in the United States

At the time the military and civilian smallpox vaccination programs began in late 2002 and early 2003, respectively, the federal government had access to two stores of smallpox vaccine: 15 million doses of Dryvax in government storage since 1982, and 70-90 million doses of Aventis Pasteur vaccine available from the company (Lueck, 2002; Roos, 2002; CDC, 2003b). Both vaccines were derived from the NYCBH strain of vaccinia virus, but Dryax was stored frozen in dry form, while the Aventis vaccine was stored frozen as a liquid. A clinical trial of Dryvax conducted by the National Institute of Allergy and Infectious Disease (NIAID) showed that the vaccine was viable and could be diluted fivefold and even tenfold and retain its efficacy, as shown by high “take” rates (Fauci, 2003; Frey et al., 2002; NIH, 2002). A later dilution study of Aventis Pasteur (also derived from the NYCBH strain) vaccine showed similarly high vaccination success rates among the three dilution groups (Talbot et al., 2004). Diluting existing vaccine and efforts to develop new vaccines provided assurance that enough vaccine would soon be available to protect all Americans in case of an attack with smallpox virus.

In 2002, changes to the diluent used for Dryvax required that the vaccine be relicensed by the Food and Drug Administration (FDA). On October 25, 2002, FDA approved a new 100-dose kit for Dryvax that included a new supply of diluent (to be mixed with the dried vaccine before it is administered) and bifurcated needles for vaccine administration (FDA, 2004). Each available lot would be approved separately. At the time civilian

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